Tuning indicator circuits



Feb. 13, 1940.

W. VAN. B. ROBERTS TUNING INDICATOR CIRCUITS Filed June 27, 1936 NETWORK AAAA INVENTOR WALTER VAN B. ROBERTS BY g ATTORNEY IIIIL IIILII .71 I tern ingeneral, being circular in shape, and having a dark space,--or gap, inthe luminous ,ring

Patented Feb.,13, 1940 UN ST OFFICE a TUN IN GbI ND IOATORn cmom'rs t'Walter van B. Roberts; Princeton, J., as-

signor -ltoaltadio. Co p rationbf America, a V corporation of Delaware"; --ApplicationJune-'27, 1936,--Seri'al"No. 87,607 1101m (crest-40 'My present invention relates totuning-indicatcr circuits for radio receivers, and more par.-

ticularly to tuning indicator 'ci'rcuitsemploying indicator tubes of the cathode ray'type. '[There has been disclosed by H. Mnwagner in "appliCatiOnQSer. No.;'28,689,-"filed June 27, 1935,

;-now issued as Patent No. 2,051,189 on August18, 1936, a tuning indicator-tube having a'fluorescent electrode which isrendered luminous, --and-has the appearance of a pattern of 1, light; the patwhich-increases in width'upon-departure-of the receiving apparatus from resonance. --di sclosed in the 'aforesaid patent, suchan indicator tube is adapted for useina radio -receiver equipped with automatic volume- -control en'd the indicator tube is'known as a-6E5-type tube. In general, automatic volume. control '(AVC) voltage is employed automatically to-regulate the width of the electrical shadow which is castupon v the fluorescent screen of'theindicator tube.

Experience with this type of: cathode ray-- indicator tube, inreceiversequipped with AVG,

demonstrates that itis not adapted to indicate thestate of resonance of the receiver-after the operator has beenaway from the receiver for a period of time. Since the' width of theshadow cast upon the luminous screen of the indicatortube depends' upon the signal strength at thereceiver, a variation in signal strength-maytwell be misinterpreted by the operator as a change: in the state of tuning. For example; if the receiver is accurately tuned to'resonance, and minimum I shadow width issecured ,on the luminoustscreen of the indicator tube, a decrease in signal strength will cause a wideningof-theshadowof theindicator tube and cause the operator to-believe that the set has become detuned. v 1- Accordingly, it may be stated that it is one of the mainobjects of -my present inventionto" provide tuning indication means for a radio-receiver equipped with AVC, wherein the indicator means is, in general, of the aforesaid tuningfiindicator tube type,- but wherein the operator: may at any time 'observethe stateof tuning of the receiver and know that the indication is independent of the receivedsignal' strength. l

Another'important object of this inventionf is to provide-in addition to a tuning ,indicatorflof the cathode ray type which is constructedtoproduce a shadow widthfdependentmupon (signal strength, an auxiliary cathoderay tube indicator means which is constructed and arranged Sothat substantially no-shaclow-will be produced: if the receiver-is in tune. Still-anotherobject of the invention is to provide a single indicator tube of the cathode ray type, -''thetube bei-ngconstructed to produce a pair ofshadows on a luminous screen, and wherein the widthof one shadow is determined by signalstrength, and thewidth of the other shadow is responsivechiefly tothe resonancecondition of the-receiver. 1

"The 'novel featureslwhichI believe to be char- "acteristic ofmy invention are set forth in 'particularity in-the; appended claims; the invention itself, however, asto' -both its organization and I method of operation willlbestbe understood by reference to the-following description taken in connectionwitlr thedrawingin which I have indicated diagrammatically two circuit organizatio ns -whereby-rny invention may be carried-into effect. v

. '20 In the drawing, I a a P Fig. 'lis a circuit diagram of a portion of a superheterodyne receiver embodying one form of =the presentinvention,

Tl'a shows: the appearance of the luminous screen ofthe indicator'tubewhich indicates si'g-' hal strength; a v

Fig; lb' is aPsimiIarVieW-Of the luminous screen of the indicator tube :which indicates solely the resonance condition of the receiver; .2 Fig. :2 is a modified form of theinvention, I Fig. 2a showsl the appearance of the luminous screen of thenndicator tube of Fi'g. 2. g :Referringnow to the accompanying drawing,

-whereinlike nference-characters in the different figures designate similar elements, in Fig l-there r is, shown schematically that portion of asuper- .hetero'dyne receiving system which is essential =.=to.antunderstandingof this invention. The-sec- 1 on'ddetectorlof the-receiving system is sho'wn as.,--;

a diode; and-its anode isconnected to its ground- :=.'ed cathodetthrou ghitheI. Frinput circuit i and theeload, -.resistor "2 arranged in series; thev load resistor '2 bei-ngshuntedby the LF. by-pass condenser 3. Therprimaryjcircuitr 4 of the I: F. con-n 5 pling transformer T is to be miderstoodza'sbeing lead is connected, through a filter resistor 5, to

put circuit. A tunable local oscillator is also pro-' vided, and it is tunable over a frequency range which differs from the desired signal frequency range by a predetermined operating I. F. The latter may be chosen from a range of 175 k. c. to 450 k. c.

The direct current voltage developed across resistor 2 is used for AVG purposes, and the AVG the anode side of load resistor 2. The AVG lead may be connected to any of the preceding signal transmission tubes in any manner well known to those skilled in this art. The audio voltage developed across resistor 2 is transmitted through condenser 6 to the audio frequency network, and the latter may be terminated by any desired type amplifier section comprisesthe grid 8, the oathode 9, and the plate III. The grid 8 is connected by the lead II to the anode side of the load resistor 2. filter network I2 for suppressing the pulsating component in the direct current voltage developed across load resistor 2. Proper energizing potentials are supplied to the indicator tube I.

from a voltage supply bleeder resistor I3, an intermediate point of which is grounded; and the cathode 9 being connected in an adjustable 'manner, as by a tap I43, to a point between ground and the negative terminal of the resistor I3. The plate Ill may be connected through a resistor I5, and an adjustable tap I6, to a desired positive potential point on resistor I3 which is above ground. I

The upper section of the indicator tube comprises a fluorescent screen, or conical anode, II. The cathode 9 is provided with a second cathode section I8, the latter being spaced from the cathode section-,9, but being maintained atthe same direct current potential as the cathode 9.- The interior surface of the anode I1 is coated with a material which becomes luminous when electrons from cathode I8 fall thereon. The control element I9 is spaced from cathode. I 8, but is arranged in parallelism therewith, and thus provides an electrical shadow at a portion of the.

luminous screen. The control element I9 is connectedby a direct current connection to the plate IILand it will assume a direct current potential which is equal to the direct current potential of the plate side of resistor I5. 1 The numeral 2i] denotes a cap positioned approximately as shown in Fig. 1, which gives to the eye of the person viewing the indication end of the tube the appearance of a luminous ring, and at the same time shields the eye from looking at the glowing cathode I8. v

In Fig. 10. there is shown the appearance of .the luminous screen of tube I when the shadow width is a maximum. This is the condition when the received signal strength'is very weak or improperly tuned in. The shadow 2| varies 'in width inversely as the received signal strength. The luminous inner face II of anode I'I appears as a luminous annulus. As the direct current voltage impressed on grid 8 varies in magnitude,

signal strength.

The lead II may include therein .9.

the width of shadow 2| will also change. This is explained by the fact that the voltage drop across resistor I5, with minimum signal amplitude impressed on circuit I,'is a maximum, and, there fore, the potential of control element I9 is at a minimum positive potential with respect to cathode I8. This means that the shadow width 2I' is a maximum. However, as the signal amplitude.

,atcircuit I increases, the bias of grid Sbecomes;

more negative with the resultv that the voltage 10 drop across resistor I5 decreases, and the-control element I9 becomes'morepositive. This re- I sults' in a decrease in the width of shadow 2i. In this'way it will be seen that the shadow 2| has; its width inversely proportional to the received The indicator tube I need not have the ampli- 'fier section constructed as a triode, and this section may be of any other multi-electrode type. The cathode sections 9 and I8 are of the equipotential type, and the control element I9 may be arod, or a vane shaped from sheet material, andplaced edgewise to. the cathode I8. The anode I7 surrounds, and is concentric with, thelike a dish pan, with an inner coating II which becomes fluorescent under electron bombardment.

The cap 20, positioned over the top end of oath ode I8, further functions to confine the electrons, and prevents electrons from reaching the glass-3 walls of the envelopeover the top of anode III.

In this type of tuning indicator the electrons travel radially outward from the cathode to the fluorescent coating II on the anode in a wide beam. The extent of the surface. of the anode reached by the electron beamis determined by the voltage on the electrode I9. The more positive' this electrode, I9 is with respectto anode I'I,

the greater is the area of-the anode coveredby,

the beam and the greater will be the area of thegflfl I This tube is to be understood as being constructed;

exactly the same as tube I. For this reason it is not, believed necessary to provide anyreference --numerals on the electrodes of tube 22. The

viewing portion of tube 22 is shown in Fig. 1b, andthe shadow 23 thereof will be a minimumi'to when the receiver is in tune. Thisaction is secured by connecting the grid of the amplifier. section of tube 22 to the cathode of diode rectifier 24 through a direct current potential connection :;including the pulsating component filter network 25;v a load resistor 26 being connected between the cathode and anode of diode 24. The cathodev and; anode of diode .24jare connected in shunt across a circuit comprising the variable tuning condenser 21 and the secondary of transformer T1. The I. F. signalenergy is impressed across the circuit 2 8-2'I--T1 by means of a trans-1" former T2.

l The variable condenser 28 tunes the secondary or transformer T2, the primary of T1 and condenser 21 to resonance so as to provide a rapid voltage rise off resonance. The energizing potentials for tube '22 are derived from the voltage bleeder resistor I3, the diode anode end of re sistor 26 being connected through an adjustable- J 'tap29 to a point on resistor I3. The cathodej of the amplifier section of the indicator tube is connected to a point on the resistor I3 that is more positive than; tap 29, and thefiuorescent screen and amplifier plate of the tube 22-. are con- 22,190,435 nctedtoza stillmore positive'zpotentialt-pointton I the bleeder :resistor, the ampliflerc plate :CiI'Olli-t including resistor 30;,

:When; :correctly tuned signals are impressed on the circuit- 21--T1, the voltage transferred.

acrossthis circuit to diode 24 will be substantially zero, since the reactance of condenser ZT-iswadjusted to be equal and opposite to the mutual reactance between the windings of T1 at.;the.:operating I. F. In this case the voltage drop. across resistor 26 'isupractically zero, and, therefore,

. shadow -23. and the signal amplitude should decrease due to fading, and the operator then returns toithe the grid of the amplifier section oftube 22 will be "negative. The voltage drop across x'resistor I 3!! willbe a certain small amount depending :on 215 the position of tap 29, with theresult that the shadow 23 will take on a'desired normal width. However, as the I. F. energy impressed :on the circuit 21-T1 departs fromythe resonantpfre-v quency, then voltage; begins to1=beimpressedion diode M'with the result thatthecathode side of resistor 26 becomes more positive,.=and the directcurrent voltage drop across resistori30 increases- This results in a widening of: .the If the operator leaves the receiver,

53?, he can immediately tell that the receiver'is still in resonance, but that the signal strength. has decreased. This follows fromthe 'factthat (80' as long as the receiver is in resonance, the. shadow will be of its normal widthgandqonly widens out when the receiver isdetuned from the-:de-

Of course, it is possible to'reverse the relation'between shadow width and signal sired signal.

amplitude, or resonance, in the case ofv tubesil and 22. In other words, by reversing the, phase of variation of the control voltages impressed-on the grids of the amplifier sections of tubes 'lzand it, the shadow 2| .of tube 1' may becaused to vary directly with signal strength, whereasth'el shadow 23Icanbe made to have a definite .norinal width which decreases when thereceiver is detuned.

In Fig. 2, I have shown -an' 'indicator tube which is adapted to produce the signalstrength indication shadow and the resonance state shadow on one viewingscreen. Thus, Fig."2a shows the shadow, whose'width is inversely proportional to ,signal strength, and theshadow 42 whose width is inversely proportional 'tosthe resonancecondition of the receiver. Furthermore, the tube 40 does not-utilizeany amplifier sections, as in the case of tubesv land 22', but employs independent amplifiers, or phase reversal tubes. Thus, the tube vMlcomprises the-fluorj escent anode 43. andv the cathode '44. One control eiectrode 45 is disposed on one side of cathode whereas the controlelectrode 46 is-disposed on the other side thereof. v v

The cap 41 functions in he manner described in connection with cap 20,.andthe bleeder -re-; sister 58 supplies the operating potentials'for the The cathode is connected 1 to an intermediate ground point on resistor. 50,

and the luminous screen 43 is connected to the positive side of bleeder 50. Thecontrol electrode is connected to the plate of the. phase invervarious electrodes.

sion tube and the gridof .the latter will "be connected to :the lead H of Fig. 1.. The "control electrode 46' is connected to the plate of the phase inversion tube Y52, and thegrid of thelatter is 0011- nected to the'cathodeside of resistor 26 which as in the-case o-fzFig. .laisiconnected across the rectifier 24, the input of' which is to be understood to be connected to the circuit appearing to 'the lft of the line: :z:-:-yin Fig. '1. Whema -sig- M. nal is tuned the .AVG bias on: the gridv 'of tube -i5l will be. a maximum; this means that the drop across the plate resistor is-a minimuman-d the 'biasiorr electrode 45 :is a minimum. Hence the li' shadow 4 I will-be very narrow, since-the electrons .from' cathode "-44 are not repelled. :At the same' "time-the drop across resistor 26is zero, because "at resonance the :potential across 21--T1: is'zero. For. this reason thetube Wis-biased toits maxif m-um extent, and the voltagedrop across -the plate resistor of tube 52 is a minimum. Consequentlythe electrode 46 is not biased, 'andit does not repel electrons to producea shadow.

= TIlhe minimunrshadow width 42 is thusproduced. If signal strength decreases due to fading the width of shadow 4| will increase, because-the electrode '45 becomes negative. 'will not change in width until the receiver is -detu'ned; and'potential appears-across resistor- 26"- du'eto rectification of voltage across T121-by The shadow rectifier 24. v

. The electrode4 5 caststhe shadow'll onzthe luminous inner face 43' of anode 43, andthis shadow becomes narrower as the received signal strength increases, as explained' heretofore. 0n the other hand, electrode produces themini- 'mum shadow :42 regardless of signal strength when the receiver is in tune. Of course-the amplifying andphase inversion tubes 5| and- 52 330 may be included in tube 40,- if 'it-is 'desired to have'the tube lfl constructed in -this-'-manner.

Howeveninorder topreserve simplicity ofconstruction in the case of tube 40, itis preferable to have the envelope include only the fluorescent 5 screen, the cathode-and the shadowproducing rods. .The potentialsofthe electrodes and M6 "determine the widths of the electrical shadows stand 42.

The signal intensity at whichthe shadow Ii -2:40

thecircuit of Fig. 1 becomeszerojmay-be-ad- --justed byvarying tap Mgor'by-varyingtap- -l 6.

In the same way the-normal shadow width'at re- While I have :iindicated and described two sysitems for carrying. my inventioninto effect, it will 55 beiapparent to one skilledinthe art-that my invention is by no. means limited tc-the particular circuit organizations shown and described, but

that many modificationslmay bemade without departingfrom' the scope of my-inventionas set forth in the appended claims.

What I claim is: i 1. Inaradio receiving systemprovidedwith a signal rectifier, means ioremploying the direct current voltage component of rectified signals as ansautomaticavolume control bias, a cathode ray indicator tubewhich includes at least a cathode and 1a fluorescent-anode, an electrode disposed in the indicator tube in-such amann'er that it is in the path-of the electrons-irom the 7"0' -ciathode tox-the anode, means responsive to-=sai'd voltage component for varyingthepotential of said -control electrode a'hd 't'he'ziiby varying :the

width of an electrical shadow produced on the fluorescent anode, a second electrode disposed in the indicator tube, and means for varying the potential of said second. control electrode chiefly in response to changes inrthe'resonance condition of thereceiveni g 2.-;In, a radioreceiving system provided with a signal rectifier, meansflfor employing the direct current voltage component of rectified signals as an automatic volume control bias, a cathode ray indicator tube which includes at least a cathmm ode and a fluorescentanode, an electrode disposed in the indicator tube insuch a manner that it is in the; path of the electrons from the. cathode to the anode, means responsive to said voltagevcomponent for varying the. potential of 15 said control. electrode and thereby varying the Width of an electrical shadow produced on the fluorescent anode, a second electrode disposed in the indicator tube, and means for varying the potential of saidsecond control electrode chiefly in response to changes in the resonance conditionof-the receiver, said last means including a resonant circuit having substantially zero voltage output vat resonance and rapidly increasing voltage output 01? resonance.

3.. In a wave signaling system, an indicato tube provided with a cathode, a fluorescent anode surrounding the cathode, and a pair of control electrodes disposed in the electron stream from thecathode .to the anode, said control electrodes 0'80 being disposed on opposite sides of the cathode,

.means responsive to variations in wave amplitude for-.jvarying the direct current potential of one'of said control electrodes and thereby varying the: width of an electrical shadow produced on said'anode by said, one control electrode, and additionaL'means responsivechiefiy to a change in the resonance condition, of the system for varying the direct current potential of the other control electrode thereby to provide a second ,f gofelectrical shadow on said-anode.

4.,In a: wave signaling system, an indicator tube provided with a cathode, a fluorescent anode surrounding the cathode, and a pair of control electrodes disposed in the electron stream from ;;45 -the cathode to the anode, said control electrodes lbeing disposed on opposite sides of the cathode, means responsive to variations in wave amplitude Iorvarying the direct current potential of one of said control electrodes and thereby vary- 5c ing the width of an electrical shadow produced on said anode by said one control electrode, and additionalmeans. responsive chiefly to a change in the resonance condition of the system for varying the direct'current potential of the other control electrode thereby to provide a second from thecathode to the anode, said control ele'c--.

c5 trodes being disposed on opposite sides of the cathode means responsive to variations in wave amplitude for varying the direct current potential of one ofsaid control electrodes and thereby varying the width, of an electrical shadow pro- :10 duced on said anode by said one electrode, additional means responsive chiefly to a change in the resonance condition of the system for varying the direct current potential of the other convareonss trol electrode therebyto provide a second e1ec-" K trical shadow .on' isaidanode, said second means including an input circuit 'tuned' to 'a' desired wave frequency and having substantially zero volt'agedeveloped thereacross at resonance, and 7 a rectifier adapted'to produce said second direct current potential from alternating currentv voltage developed across saidresonant input circuit 01f resonance.

6. In a radio receiver provided with a signal} rectifier, means for employingthe direct current voltage component of rectified signals as an au "tomatic volume control bias, cathode ray indi- I cator means capable of producing a pair of in-J dependent electrical shadows, means responsive to variations in automatic volume control bias for varyingth'e' width of one of saidelectrical shadows, and -means responsive chiefly to er forvaryingthe width of the other, electrical shadow.

7. In a radio receiver having a signal channel *changes in the resonance condition of thereceivj which includes Ia rectifier, means forderiving from the rectifier a direct-current voltage capable of being utilized as an automaticvolume control. bias, means for visually indicating variations from the signal channel a direct current voltage which varies chiefly with the resonance condi l '30 the first visual indicating means'ior visually indicating variations in said last mentioned de-*' rived voltage.

tion of the receiver, and means independent of 8. The invention defined in claim 7 wherein each of the visual indicating means compri'ses' a' in saidderived bias voltage, means for deriving cathode ray indicator tube provided with a cathode; a. ray-control electrode and a fluorescent anode, eachof said derived voltages being applieda to one of the ray-control electrodes of said cathode ray tubes.

. 9.'The invention defined in claim 7 wherein said visual indicatingmeans are included in a M common cathode ray indicator tube which is provided with a cathode, apair of ray-control'eled trodes and a fluorescent anode,each of said derived voltages vbeing'applied to one of saidpair of ray-control electrodes.

10. In a wave signalling system, a'pair of indicator'tubes each provided with a cathode, a

fluorescent anode surrounding the cathode and v a ray-control electrode. disposed in the electron stream between cathode and anode, means responsive to variations in wave amplitude for varying the direct current potential of the raycontrol electrode of one of. the indicator tubes and thereby varying the width of the electrical shadow produced on the anode of said indicator .tube, and additional 'means responsive chiefly to a change in the resonance condition of the "system for varying the direct current potential --of the ray-control electrode of the other indicator tube thereby to provide an electrical shadow on the anode of said other indicator tube.-

11. The invention defined in-claim 10 wherein the additional means includes an input circuit sharply tuned to the operating frequency" and produce said second direct current potential from alternating currentvoltage developed across said resonant input circuit 01f resonance.

WALTER, VAN ROBERTS.

has substantially zero voltage developed thereacross at resonance, anda rectifier adapted to 

